1. Field of the Invention
Means are provided for selecting out of the twelve tones of an octave those needed for any mode of the diatonic scale, and for selecting different musical scales.
2. Description of the Prior Art
During the twentieth century, most keyboard musical instruments in the United States have been tuned in an equitempered scale with twelve tones per octave. In the ideal equitempered scale, the fundamental frequencies of two consecutive tones differ by a factor equal to the twelfth root of two. Although no real instrument can be tuned exactly in the ideal equitempered scale, it is common to tune keyboard musical instruments in a twelve tone scale such that any two consecutive tones will have the ratio of their fundamental frequencies equal to the twelfth root of two within about one percent. The resulting musical scale may be called a nominally equitempered scale. The musical intervals between adjacent tones of the scale are considered to be equal to each other, and each of them is called a semitone.
Traditionally, keyboard instruments play seven of the twelve tones per octave on the front digitals of the keyboard, and the other five tones on the back digitals. Eight successive front digitals of the keyboard play the diatonic scale, the major mode of the diatonic scale being defined by the intertone musical intervals 2--2--1--2--2--2--1 semitones. In the United States, the labels commonly associated with the tones of the major mode of the diatonic scale are do-re-mi-fa-so-la-ti-do. When this mode is played on the keyboard in the key of C, the corresponding labels for the front digitals and for the tones they play are C-D-E-F-G-A-B-C.
In the traditional system of music notation, the C,D,E,F,G,A,B tones are represented by notes on the lines and spaces of a five line staff. An intermediate tone is represented by one of the above notes of the diatonic scale, together with a .music-sharp. symbol or a .music-flat. symbol serving as a tone correction to that diatonic tone. Thus, a tone intermediate to the C and D tone is represented as C.music-sharp. or D.music-flat., and it is played by a back digital positioned between the C and D front digitals.
For a musical composition to be played entirely on the front digitals of a conventional organ, it must be written in the diatonic key of C. A restraint such as this would severely limit a composer's freedom, for he probably wants to base the major mode of his scale on a tone above or below the absolute pitch of C.
In principle there are two ways to move the diatonic scale from one absolute pitch to a different absolute pitch. The preferred way for keyboard instruments would be to specify a movable C major scale in which the pitches played by all digitals are bodily moved a specified distance upward or downward -- say four semitones upward. This method has not been available to past composers and their publishers, because most musical instruments have not possessed the pitch changing device which is required for this method.
A less satisfactory second method for specifying the absolute pitch of the diatonic scale is generally used by composers; they start the major mode of the diatonic scale on a front digital above or below the C digital. This method requires that one or more of the back digitals of the keyboard be included in the diatonic scale. For a given pitch of the major mode of the diatonic scale, the same back digitals must always be included. Consequently, the composer finds it convenient to include these particular sharps or flats in a key signature that is placed at the front of each line of written music.
The composer can start the major mode of his diatonic scale on any one of the seven front digitals in an octave span, and he can use either all flats or all sharps with each digital. Thus he uses fourteen different key signatures in addition to the key of C, which requires neither sharps nor flats.
The inexpert player has difficulty remembering and playing the sharps or flats called for in all those key signatures. To alleviate this difficulty, a keyboard instrument can be provided with a device to physically actuate the digital corrections included in the key signature. Such a device, called a key selector, can be set to the key signature by the musician; after that he can play the diatonic scale on the front digitals.
Philipps, in U.S. Pat. Nos. 466,907 and 519,071, has disclosed mechanical key selectors that can be set to physically actuate the key signatures of written music. When the device is set for a key signature with one flat, for example, the effects of the B and B.music-flat. digitals are interchanged so that the B digital plays the B.music-flat. tone. Thus, the player strikes the B digital, as indicated by a note on the staff, and gets the sound of B.music-flat.. If, in the written music, the player encounters a B natural sign, he must get the B natural tone by striking the B.music-flat. digital.
A second type of key selector has been disclosed by Cornelius in U.S. Pat. No. 2,484,930. The Cornelius key selector has the advantage of keeping all tones in order on the keyboard so that the pitch played by each digital is higher than the pitch played by digitals on its left. This apparatus has cam-operated electrical switches associated with each digital; it has the disadvantage of requiring a major mechanical modification of the keyboard which provides two extra back digitals per octave span. If crowding at the back of the keyboard is to be avoided, the size of an octave span must be increased from about 164 mm to about 191 mm.
While the composer has made known the preferred absolute pitch of his musical composition by the location of his notes on the staff and by his key signature, the keyboard player may need to change the absolute pitch. He may need to accompany a singer or another musical instrument with a limited range of absolute pitch. A change of pitch can be accomplished without changing the key digital if a pitch changer is available which raises the pitch coupled to each digital by a fixed musical interval, such as four semitones. Many inventors have described pitch changers to be used by the keyboard player for this purpose.
The switches that I call pitch changers do not change the musical interval between tones played by adjacent digitals, which I call the interdigital intervals. For example, the interdigital musical interval between the C and D digitals is two semitones in the state of standard pitch, and it remains two semitones in all states of the pitch changer. Similarly, the interdigital musical interval between the B and C digitals remains one semitone in all states of the pitch changer. This characteristic of interdigital invariance distinguishes pitch changing switches from other members of the class of tone transposition switches. So far as I am aware, publically described electronic tone transposition switches all belong to this subclass of interdigital invariant switches.
The class of interdigital invariant switches can utilize simple constructions which are not available to the general class of tone transposition switches. An example is disclosed in my U.S. Pat. No. 3,949,638. In this simple pitch changer, a linear array of contacts permanently coupled to the digitals slides along a linear array of contacts permanently coupled to the tone generator circuits. Other examples of simple pitch changer structure are disclosed in U.S. Pat. Nos. 3,610,800 -- DEUTSCH and 3,836,909 -- COCKERELL.
An organ having an electronic switch that changes the interdigital musical intervals is disclosed but not claimed in my U.S. Pat. No. 3,943,811 column 8, lines 32 to 59 and FIG. 14. This electronic switch is used to select between the diatonic scale and the tonal pentatonic scale to be played on the front digitals of the keyboard. The application for that patent was copending with this application.
An electronic switch for selecting between the diatonic scale and a hexachord scale to be played on the front digitals was disclosed in my U.S. Pat. No. 3,973,460.